Very nice design! One point though, you can’t be serious about building the spiral clockwise in the northern hemisphere. Water will drain as a function of gravity, not the Coriolis Effect which describes the natural rotation of air or water due to the earths rotation. This effect only occurs with large masses over a very long time frame. Water draining out of a tub will rotate in one direction or other by virtue of tub shape or the way the water is entering the vessel. The same toilet will flush the same direction in New England as in New South Wales.